obstacle2
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So it's definitely been awhile since I've done geometric series but i need to use it for a bit of uni work!

I have this: a + a/(1+r) + a/[(1+r)^2] + a/[(1+r)^3] + a/[(1+r)^4]

I know how to go about deriving a general formula for an infinite series but what about this finite one? Help is appreciated!
Thanks!
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SimonM
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a+ak+\cdots ak^n = \frac{a(k^{n+1}-1)}{k-1}

To prove it, multiply by k and subtract.

In your case we obtain: \frac{a((1+r)^{-5}-1)}{(1+r)^{-1}-1} = \frac{a((1+r)-(1+r)^{-4})}{r}
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obstacle2
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(Original post by SimonM)
a+ak+\cdots ak^n = \frac{a(k^{n+1}-1)}{k-1}

To prove it, multiply by k and subtract.

In your case we obtain: \frac{a((1+r)^{-5}-1)}{(1+r)^{-1}-1} = \frac{a((1+r)-(1+r)^{-4})}{r}
Great! Thanks a lot!
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